An increased frequency of cancer has been reported for heterozygous carriers of the genes for Fanconi anemia and ataxia-telangiectasia, autosomal recessive diseases which carry a high malignancy risk for homozygotes. We will evaluate the risk to heterozygous carriers of balanced translocations, and of the protease inhibitor (alpha-1-antitrypsin deficiency) allele Piz. Specific procedures will be followed for each category of genetic disorder. The families of children with unbalanced translocation will have their chromosomes reevaluated with fluorescence, trypsin-Giemsa and reverse banding. Families of children identified either directly or through a retrospective study of liver disease will be genotyped for Pi alleles. Detailed family histories will be obtained and pedigrees constructed. The families will be HLA typed. All pedigrees will be analyzed for an increase in cancer in proven or probable carriers. Combined data will be compared to U.S. mortality statistics. All families with an increased incidence of cancer will be analyzed for association of cancer and HLA genotype. In addition to defining the frequency of neoplasia, we hope to identify some interacting factors which may influence the development of malignancy in particular genotypes.